Air bag restraining systems in vehicles for vehicle occupants are known in the art. An air bag restraining system may include a multistage inflator device where the stages are actuated at different times in response to sensed vehicle crash conditions.
U.S. Pat. No. 5,935,182 to Foo et al., assigned to TRW Inc., discloses a method and apparatus for discriminating a vehicle crash condition using virtual crash sensing. U.S. Pat. No. 6,036,225 to Foo et al., assigned to TRW Inc., discloses a method and apparatus for controlling a multistage actuatable restraining system in a vehicle using crash severity index values. U.S. Pat. No. 6,186,539 to Foo et al., also assigned to TRW Inc., discloses a method and apparatus for controlling a multistage actuatable restraining device using crash severity indexing and crush-zone sensors. U.S. Pat. No. 6,529,810 to Foo et al., also assigned to TRW Inc., discloses a method and apparatus for controlling an actuatable multistage restraining device using switched thresholds based on transverse acceleration.
The use of safing functions in the control of actuatable restraining devices is also known in the art. Early known systems used a discrimination inertia switch and a series connected safing switch. When both the discrimination switch and the safing switch closed, the restraining device was actuated. Other known systems included a crash accelerometer, a discrimination algorithm for analyzing the crash accelerometer output signal, and a sating switch. When the discrimination algorithm determined a deployment crash event was occurring and the safing switch closed, the restraining device was actuated. Still other known systems used a discrimination crash acceleration sensor oriented in a direction of expected crash and a safing crash acceleration sensor oriented in the same direction. Associated algorithms process the signals from the two sensors and control the restraint when both determined a deployment crash event was occurring.